1. Technical Field
The invention relates to aircraft capable of hovering, and capable of long-duration flight on the order of days.
2. Background of the Related Art
Previous aircraft designs have generally been optimized for relatively rapid transport of cargo from one point to another, or over an intervening region. Such aircraft, which have generally included an onboard crew, have not been suitable for long-duration missions, such as missions taking multiple days.
Air ships tend to be expensive to operate, and tend to be more fragile than many other types of aircraft, such as fixed wing aircraft. Also, air ships may be difficult to handle, especially in high winds. Further, air ships tend to be relatively slow compared with other types of aircraft.
Helicopters are one type of aircraft that is capable of hovering during flight. However, helicopters are highly stressed machines which require extensive maintenance. In addition, helicopters have poor fuel efficiency, which limits their flight time to less than that of fixed wing conventional aircraft. In addition, helicopters tend to have poor high altitude performance, when compared with other types of aircraft.
None of the prior types of aircraft described above are suitable for long-duration missions at high altitudes, especially where the missions may involve staying in substantially the same location for long periods of time.